The present invention is related to Japanese patent application No. Hei. 11-365034, filed Dec. 22, 1999; the contents of which are incorporated herein by reference.
The present invention relates to a control mechanism for reducing electric power consumption of a vehicle air-conditioning system, and more particularly, to a control mechanism for reducing electric power consumption of a vehicle air-conditioning system having an air-conditioning compressor selectively driven by a vehicle engine or a motor while the air-conditioning compressor is driven by the motor.
In a typical prior art vehicle air-conditioning system, a compressor is driven by a drive force transmitted from a vehicle engine via a belt to circulate a refrigerant within a refrigeration cycle. Thus, in a vehicle (eco-run car) that has the compressor driven by the described drive mechanism and also has a feature to automatically stall the engine while the vehicle is not running to protect the surrounding environment from the engine emissions, the compressor stops when the engine is stalled, resulting in stopping of the air-conditioning.
This fact constitutes one reason for preventing wide spread use of the eco-run cars. To address this disadvantage, Japanese Unexamined Utility Model Publication No. 60-155724 and No. 6-87678 discloses use of a motor for driving the compressor while the vehicle is not running. The motor is powered from a battery that is charged by a generator. The generator is driven by the engine while the vehicle is running.
In the prior art disclosed in the above publication, since the compressor is driven by the motor while the vehicle is not running (while the engine is not operated), a large capacity battery is required for supplying enough electric power to the motor.
If the large capacity battery is not provided, the engine must be restarted within a short period of time after the engine stall in order to prevent excessive discharge of the battery due to the power consumption of the motor during the non-running period of the vehicle. This fact deteriorates an advantageous fuel saving feature of the eco-run car.
It is therefore an objective of the present invention to reduce the power consumption of a vehicle air-conditioning system having a compressor selectively driven by a vehicle engine or a motor while the compressor is driven by the motor.
Another object of the present invention is to achieve a good balance between the power consumption reduction and a feeling of coolness in a vehicle air-conditioning system having a compressor selectively driven by a vehicle engine or a motor while the compressor is driven by the motor.
Another object of the present invention is to achieve a good balance between the power consumption reduction and anti-fogging performance in a vehicle air-conditioning system having a compressor selectively driven by a vehicle engine or a motor while the compressor is driven by the motor.
A further object of the present invention is to appropriately reduce the power consumption based on the amount of remaining charge in a battery in a vehicle air-conditioning system having a compressor selectively driven by a vehicle engine or a motor while the compressor is driven by the motor.
In a first aspect of the invention, to achieve the above objectives, a capacity of a blower and a capacity of a compressor are arranged in a refrigeration cycle while the compressor being driven by a motor is reduced in comparison to the capacity of the blower and the capacity of the compressor while the compressor is driven by a vehicle engine. Furthermore, while a cooling heat load of an evaporator is greater than a predetermined value, the capacity of the compressor is first reduced prior to reducing the capacity of the blower.
The capacity of the blower can be indicated by the amount of the air flow per unit time. The capacity of the compressor can be indicated by the amount of the refrigerant discharged from the compressor per unit time. When a variable displacement compressor is used as the compressor of the present invention, the capacity of the variable displacement compressor can be changed by adjusting a displacement of the variable displacement compressor. When a fixed displacement compressor is used as the compressor of the present invention, a capacity of the fixed displacement compressor can be changed by adjusting a ratio between an xe2x80x9cONxe2x80x9d period and an xe2x80x9cOFFxe2x80x9d period (utilization rate) of the fixed displacement compressor. Furthermore, when the compressor is driven by the motor, the capacity of the compressor can be changed by controlling a rotation speed of the motor. Either the capacity of the blower or the capacity of the compressor while the compressor is driven by the motor is reduced.
Furthermore, while the cooling heat load of the evaporator is greater than the predetermined value, the capacity of the compressor is first reduced prior to reducing the capacity of the blower. Thus, when the cooling heat load of the evaporator is high, for example, when the outside air temperature is high during the summer, the power saving can be achieved by reducing the capacity of the compressor while maintaining the large capacity of the blower.
When the cooling heat load of the evaporator is high, rather than providing a lower temperature of the cool air blown out from the air-conditioning system, the higher air flow rate of the cool air should be provided to maintain the feeling of coolness.
In another aspect of the invention, at least the capacity of the blower or the capacity of the compressor while the compressor being driven by the motor is reduced in comparison to the capacity of the blower and the capacity of the compressor while the compressor being driven by the vehicle engine. Furthermore, while the compressor is driven by the motor, if the window glass of the vehicle is under a fog inducing condition, the capacity of the blower is first reduced prior to reducing the capacity of the compressor.
Furthermore, while the window glass of the vehicle is under the fog inducing condition, the capacity of the blower is first reduced prior to reducing the capacity of the compressor, so that, for example, under the low outside air temperature condition during the winter, power saving can be achieved by reducing the capacity of the blower while maintaining the large capacity of the compressor. As a result, the high dehumidifying capacity of the evaporator is maintained, and therefore the high anti-fogging performance of the air-conditioning system for preventing fogging of the vehicle window can be adequately provided.
In another aspect of the invention, while a blow mode is set to provide directional air toward the window glass of the vehicle, the capacity of the blower is not reduced even if it is determined that the window glass of the vehicle is under the fog inducing condition.
While the blow mode is set to providing directional air toward the window glass of the vehicle, the capacity of the blower is not reduced, so that the anti-fogging performance can be maximized at the sacrifice of power saving. As a result, fogging of the window glass of the vehicle can be cleared within a short period of time even while the compressor is driven by the motor (i.e., even while the engine is not operated).
In another aspect of the invention, there is provided means for changing the capacity of the compressor in a gradual manner. A rate of gradual change of the capacity of the compressor while the compressor being driven by the motor is set to be higher than that of the compressor while the compressor being driven by the vehicle engine.
With this arrangement, when the capacity of the compressor is reduced while the compressor is driven by the motor, the capacity of the compressor can be quickly reduced to improve the power saving.
In another aspect, the capacity of the compressor is adjusted to make an actual degree of coolness of the evaporator to coincide with a target value. A rate of change of the target value while the compressor being driven by the motor is increased in comparison to the rate of change of the target value while the compressor being driven by the vehicle engine, so that the rate of the gradual change of the capacity of the compressor can be increased.
Since the rate of change of the target value while the compressor being driven by the motor is increased, the capacity of the compressor can be reduced quickly to improve power saving.
In another aspect of the invention, the compressor is a variable displacement compressor, and the capacity of the compressor is changed by changing the displacement of the variable displacement compressor. With this arrangement, the capacity of the variable displacement compressor can be reduced quickly to improve the power saving.
In another aspect of the invention, a computing means is provided for computing a control output value, which determines the displacement of the compressor, based on a deviation between the actual degree of coolness of the evaporator and the target value. A rate of change of the control output value computed by the computing means relative to the deviation while the compressor being driven by the motor is increased in comparison to the rate of change of the control output value computed by the computing means relative to the deviation while the compressor being driven by the vehicle engine.
With this arrangement, when the control output value for controlling the displacement of the compressor is computed, the rate of change of the control output value is increased while the compressor is driven by the motor. As a result, the rate of gradualxe2x80x94change in the displacement control can be increased to improve the power saving.
In another aspect, there is provided means for gradually changing the capacity of the blower for blowing the air toward the interior of the vehicle. A rate of gradual change of the capacity of the blower while the compressor being driven by the motor is increased in comparison to the rate of gradual change of the capacity of the blower while the compressor being driven by the vehicle engine.
In another aspect of the invention, the capacity of the blower or the capacity of the compressor arranged in the refrigeration cycle while the compressor being driven by the motor is reduced in comparison to the capacity of the blower and the capacity of the compressor while the compressor being driven by the vehicle engine. Furthermore, while the compressor is driven by the motor, at least one of a degree of the reduction of the capacity of the blower and a degree of the reduction of the capacity of the compressor is controlled based on the amount of remaining charge in a battery that provides power to the motor.
With this arrangement, the degree of the reduction of the capacity of the blower and/or the degree of the reduction of the capacity of the compressor can be adjusted to an appropriate level corresponding with the amount of the remaining charge in the battery while the compressor is driven by the motor.
Therefore, large power consumption that depletes the remaining charge in the battery within a short period of time can be predicted. If large power consumption is predicted, the amount of reduction of the capacity of the blower and the reduction of the capacity of the compressor can be increased to reduce the power consumption. As a result, large power consumption while the compressor being driven by the motor can be prevented to avoid restart of the engine shortly after the engine is stalled.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.